Sleep is controlled by two biological processes, the homeostatic drive and the circadian rythym. The homestatic drive manifests itself as an increased drive for sleep. This drive for sleep accumulates across the period of wakefulness (typically daytime) and dissipates across the sleep period. The circadian rhythm of sleep-wake shows a biphasic curve with the greatest drive for sleep occurring between midnight and 5 AM, and between 2 PM and 4 PM. It is believed that major circadian influences are an alerting pulse in the evening and in the morning. It is the interaction of these processes which give rise to the 24-hour sleep schedule. For individuals with a usual sleep period of 11 PM to 7 AM, sleep onset in the evening occurs primarily as a function of homeostatic drive. After about four hours of sleep (at about 3 AM) homeostatic drive dissipates significantly and wakefulness begins to intrude into the sleep period. This propensity to increased wakefulness is further increased by the rise in the circadian alerting pulse at about 5 AM. In terms of the pharmacological management of insomnia, two vulnerabilities have been recognized. The first is difficulty initially falling asleep, with the second being reawakening in the middle of the night.
Many physiological functions are characterized by diurnal rhythms, in which levels of circulating hormones, catecholamines and other compounds fluctuate during the day and/or night. Certain medical disorders, such as insomnia, are associated with abnormalities in these rhythms. The time, within a 24 hour period, of administration of drugs for the prevention and treatment of such disorders can be a critical factor in determining efficacy of the therapy.
The term “insomnia” refers to the perception of inadequate or non-restful sleep by a patient. Insomnia is a frequent complaint, reported by 32% of the adult population surveyed in the Los Angeles area (Bixler et al, Amer. Journal of Psychiatry 136:1257-1262, 1979), and 13% of the population surveyed in San Marino, Italy (Lugaresi et al., Psychiatric Annals 17:446-453, 1987). Fully 45% of the surveyed adult population of Alachua County, Fla., reported trouble getting to sleep or staying asleep (Karacan et al., Social Science and Medicine 10:239-244, 1976). The prevalence of insomnia has also been shown to be related to the age and sex of the individuals, being more prevalent in older individuals, especially adults aged 65 and over, and in females.
Early treatments for insomnia commonly employed central nervous system (CNS) depressants such as barbiturates. These compounds are typically long acting (on the order of 8-50 hours) due to long terminal half-lives, and have a well-known spectrum of side effects, including lethargy, confusion, depression and next day hangover effects. In addition, chronic use has been associated with a high potential for addiction involving both physical and psychological dependence.
During the 1980s, the pharmaceutical treatment of insomnia shifted away from barbiturates and other CNS depressants toward the benzodiazepine class of sedative-hypnotic agents. This class of compounds produces a calming effect that results in a sleep-like state in humans and animals, with a greater safety margin than prior hypnotics. However, many benzodiazepines possess side effects that limit their usefulness in certain patient populations. These problems include synergy with other CNS depressants (especially alcohol), the development of tolerance upon repeat dosing, dependency, withdrawal, rebound insomnia following discontinuation of dosing, hangover effects the next day and impairment of psychomotor performance and memory. Next day sleepiness and memory impairment, which can include amnesia for events occurring prior to and after drug administration, is of particular concern in the elderly whose cognitive functions may already be impaired by the aging process.
More recent treatments for insomnia have used non-benzodiazepine compounds, which show an improved side effect profile over the benzodiazepine class of sedative-hypnotics. The first of these agents to be approved by the United States Food and Drug Administration (FDA) for marketing in the United States was zolpidem, marketed by Sanofi-Synthelabo as AMBIEN® (zolpidem tartrate), which is based on the imidazopyridine backbone (see U.S. Pat. Nos. 4,382,938 and 4,460,592). In addition to zolpidem, zaleplon, which is marketed by Jones Pharma as SONATA®, was been approved by the FDA; zaleplon is a pyrazolopyrimidine-based compound (see U.S. Pat. No. 4,626,538). Other non-benzodiazepine compounds and/or methods for making or using the same have also been reported (see, e.g., U.S. Pat. Nos. 4,794,185, 4,808,594, 4,847,256, 5,714,607, 4,654,347; 5,538,977, 5,891,891). Attempts have also been disclosed to provide controlled-release dosage forms, particularly in the context of zolpidem and salts thereof (see WO 00/33835 and EP 1 005 863 A1).
Norepinephrine and serotonin are mammalian neurotransmitters that play important roles in a wide variety of physiological processes. Norepinephrine, also called noradrenaline, is a neurotransmitter that doubles part-time as a hormone. As a neurotransmitter, norepinephrine helps to regulate arousal, dreaming, and moods. As a hormone, it acts to increase blood pressure, constrict blood vessels and increase heart rate—responses that occur when we feel stress.
Serotonin (5-hydroxytryptamine, 5-HT) is widely distributed in animals and plants, occurring in vertebrates, fruits, nuts, and venoms. A number of congeners of serotonin are also found in nature and have been shown to possess a variety of peripheral and central nervous system activities. Serotonin may be obtained from a variety of dietary sources; however, endogenous 5-HT is synthesized from tryptophan through the actions of the enzymes tryptophan hydroxylase and aromatic L-amino acid decarboxylase. Both dietary and endogenous 5-HT are rapidly metabolized and inactivated by monoamine oxidase and aldehyde dehydrogenase to the major metabolite, 5-hydroxyindoleacetic acid (5-HIAA).
Serotonin is implicated in the etiology or treatment of various disorders, particularly those of the central nervous system, including anxiety, depression, obsessive-compulsive disorder, schizophrenia, stroke, obesity, pain, hypertension, vascular disorders, migraine, and nausea. Recently, understanding of the role of 5-HT in these and other disorders has advanced rapidly due to increasing understanding of the physiological role of various serotonin receptor subtypes.
Neurotransmitters (NTs) produce their effects as a consequence of interactions with cellular receptors. Neurotransmitters, including serotonin, are synthesized in brain neurons and stored in vesicles. Upon a nerve impulse, they are released into the synaptic cleft, where they interact with various postsynaptic receptors. The actions of 5-HT are terminated by three major mechanisms: diffusion; metabolism; and uptake back into the synaptic cleft through the actions of specific amine membrane transporter systems. The major mechanism by which the action of serotonin is terminated is by uptake through presynaptic membranes. After 5-HT acts on its various postsynaptic receptors, it is removed from the synaptic cleft back into the nerve terminal through an uptake mechanism involving a specific membrane transporter in a manner similar to that of other biogenic amines. Thus, the actions of 5-HT, or any neurotransmitter, can be modulated by agents that: stimulate or inhibit its biosynthesis; agents that block its storage; agents that stimulate or inhibit its release; agents that mimic or inhibit its actions at its various postsynaptic receptors; agents that inhibit its reuptake into the nerve terminal; and agents that affect its metabolism.
Accordingly, there is a need in the art for serotonin reuptake inhibitor-sedative, norepinephrine reuptake inhibitor-sedative, 5-HT2A modulator-sedative, and dopamine reuptake inhibitor-sedative compositions that induce and maintain sleep as single dose nocturnal formulations, but without the side effects associated with the longer-acting hypnotics. The present invention fulfills this need and further provides other related advantages.